Selected luminescent molybdates and tungstates of sc., la, eu, gd, and lu



United States Patent 3,328,311 SELECTED LUMINESCENT MOLYBDATES ANDTUNGSTATES OF Sc, La, Eu, Gd, and Lu Hans J. Borcliardt, Wilmington,Del., assignor to E. I. du Pont tie Nernours and Company, Wilmington,DeL, a corporation of Delaware No Drawing. Filed May 5, 1965, Ser. No.453,502 17 Claims. (Cl. 252301.5)

This application is a continuation-in-part of copending application Ser.No. 264,065, filed Mar. 11, 1963 (now abandoned), which is acontinuation-in-part of application Ser. No. 186,602, filed Apr. 6,1962, now Patent No. 3,- 250,722, which is a continuation-in-part ofapplication Ser. No. 150,477 filed Nov. 6, 1961 (now abandoned).

The present invention relates to novel luminescent compositions, andmore particularly to such compositions containing rare earth elementsand molybdenum or tungsten.

The novel luminescent compositions of the present invention consist ofmixed oxide compounds of a selected rare earth element and tungsten ormolybdenum and certain solid solutions of selected rare earth elementsassociated with a common tungsten or molybdenum component. The rareearth elements used in this invention are scandium, lanthanum,gadolinium, lutecium, europium, samarium or dysprosium. The compounds ofthe present invention are Sc O .3WO 3Sc O .WO Eu O .3WO Gd2O .3WO3,L112O3.3WO3, La O3.WO3, GdgOg-WO3,

L11 O .3MoO La O .2MoO The solid solutions of the present invention aresolid solutions of La O .3WO or Gd203-3WO3 OI wherein the content of LaO .3WO or Gd O .3WO ranges from about 90 to about 99 mole percent. Thesesolid solutions can be represented by the formulae (La Sm O .3WO

and (Gd Dy O- .3WO wherein x is about from 0.01 to 0.10. The solidsolutions of this invention can be viewed as a crystal lattice oflanthanum or gadolinium tungstate in which a portion of the lanthanumatoms or gadolinium atoms in the crystal lattice are replaced bysamarium or dysprosium. Thus, the solid solution can be viewed as aone-phase system in which a portion of the lanthanum atoms in thecrystal lattice are replaced by samarium atoms.

The rare earth compounds and solid solutions of this invention describedabove can be characterized by conventional X-ray powder diffractiontechniques. X-ray spectra can be conveniently determined on a NorelcoX-ray diffraction unit using a recording spectrometer, CuK, radiation, 1slits, a nickel filter and a scan rate of 1 of Zqb/min. If greaterresolution is desired, a Guinier camera can be employed. As isrecognized in the art, X-ray powder patterns may not reveal the presenceof a phase unless about 5% of that phase is present. Accordingly, it ispossible, though not probable, that stated formulae indicated herein maydeviate by an amount consistent with the aforementioned limitation andshould be so interpreted.

The X-ray patterns of each of the compositions of this invention arecharacteristic thereof and are mereut from the patterns of the reactantsleading to their formation and, in the solid solutions of thisinvention, different from the individual tungstate components thereof.For instance, the ditfraction pattern for Sc O .3WO is different fromand not the summation of the patterns for Sc O and W0 The novelcompositions of the present invention are chemical compounds and solidsolutions of chemical compounds as shown by X-ray diffraction spectraand not mixtures of the rare earth oxides with tungstic oxide ormolybdic oxide. The complete X-ray diffraction patterns for two of thecompounds of this invention are given in Tables I and II. Thesediffraction patterns are considerably different from the patterns of W0M00 Gd O $0 0 or mixtures thereof. When an excess of any one of theconstituents used in making the compound is mixed with the compound, theX-ray diffraction pattern of the mixture contains lines characteristicof the compound and of the constituent added.

TABLE I.XRAY DIFFRACTION PATTERN FOR SCZO3.3WO3 d: I/I d: I/I 6.505 113.252 11 5.940 23 3.070 28 4.691 8 2.989 14 4.480 44 2.947 15 4.227 582.877 4 4.019 82 2.824 12 3.966 2.728 28 3.863 24 2.650 10 3.668 252.612 13 3.587 60 2.479 21 3.361 24 2.319 10 3.287 12 2.287 21 TABLEII.-X-RAY DIFFRACTION PATTERN FOR Gdg03.3l\1003 a; 7/1 d: 17/1 10.57 141.779 12 6.03 14 1.765 8 5.32 100 1.752 8 5.17 4 1.735 2 4.652 32 1.7284 4.304 5 1.707 3 4.062 1 1.689 10 3.934 2 1.685 11 3.714 36 1.649 63.666 41 1.645 6 3.553 97 1.621 4 3.469 46 1.610 9 3.278 38 1.592 43.197 7 1.573 5 3.134 8 1.492 3 3.095 3 1.474 7 3.019 51 1.465 3 2.93234 1.441 4 2.793 21 1.428 2 2.668 10 1.414 3 2.592 9 1.410 3 2.550 31.402 2 2.517 2 1.398 2 2.412 5 1.391 3 2.384 a 8 1.359 3 2.319 11 1.3413 2.131 4 1.337 5 2.094 10 1.321 2 2.071 3 1.304 2 2.050 4 1.302 3 2.0335 1.295 3 2.016 22 1.277 2 1.975 22 1.273 2 1.945 11 1.260 4 1.900 31.238 2 1.860 2 1.225 2 1.842 3 1.219 2 1.836 3 1.211 3 3 TABLEII.Continued a': I/I d: I/l 1.208 4 1.118 3 1.189 3 1.109 2 1.178 21.070 2 1.159 3 1.049 2 1.156 2 1.047 2 1.150 2 1.035 2 1.134 3 1.015 2Lattice constants:

a: 103691.005 A. b: 103691005 A. c=l0.672i.005 A.

The compounds of this invention are prepared by mixing startingmaterials comprising the rare earth component and a component whichcontributes M00 or W0 and thereafter heating the resulting mixture atelevated temperatures. The solid solutions of this invention can beprepared in a similar manner, or alternately, preformed rare-earthtungstates can be mixed and heated at elevated temperatures. A reactiontemperature of at least about 700 C., and usually at least about 900 C.,is employed; however, since the reaction time decreases as the reactiontemperature increases, to insure complete reactions in practical periodsof time, high reaction temperatures approaching, e.g., within 100 C. of,but in any case below, the temperature at which localized fusion of thereaction mass begins are preferred. If relatively low-melting eutecticsare formed during the reaction, it may be desirable to heat the reactionmixture for a period at, e.g., 700900 C., then regrind the resultingproduct and finish the reaction at higher temperature.

The rare earth components are preferably introduced into the reactionmixture as oxides. However, rare earth components which decompose to theoxide on heating, for example, rare earth hydroxides, oxalates,carbonates, citrates, acetates, and tartrates can be employed The W0 orMoO -contributing component also is preferably introduced in the form ofan oxide such as tungsten oxide or molybdenum oxide. However, thisreactant need not necessarily be in the form of an oxide. It can be, forexample, in the form of a compound such as tungstic acid, or molybdicacid, or ammonium tungstate, which on ignition is converted to theoxide. Reactants are preferably introduced in the form of finely groundparticulate material, preferably having a particle size of less than 10microns.

The quantities of reactants employed in preparing the compositions ofthis invention are preferably approximately stoichiometric based on thedesired composition of the final product. Thus, for example, inpreparing 3Sc O .WO three moles of Sc 0 would beheated with one mole ofW0 The compositions of this invention are all solid materials useful asinsulating bodies. Table III gives the electrical properties of apressed pellet of one representative compound of this invention.

TABLE III.-ELECTRICAL PROPERTIES OF A MIXED OXIDE COMPOUND Gd2Oa.3M0O

Sample density (g./rnl.) 1 4.25

Resistivity (ohm/cm.) 10

Dielectric constant 8.8

Dissipation factor (percent) 0.80

1 Density of pressed pellet, not true density.

Insulating bodies can be prepared, for example, by fusing thecomposition selected, for example Gd O .3MoO in a mold and coolingcarefully to obtain an insulator of the desired shape. Conductive metalsmay be coated with an insulating coating by the same technique providedthat the melting point of the metal is higher than the fusiontemperature of the mixed oxide composition. Conventional powdercompaction techniques at temperatures below the melting point followedby sintering of the powder can also be used for fabricating insulatingbodies from the compounds of the present invention. Techniques forfabricating insulators are described in, for example, McGraw-HillEncyclopedia of Science and Technology, Vol. 7, pp. 158-163 (1960).

The compositions of this invention described above can also be used informing brightly luminescent solid solutions such as those described incopending application Ser. No. 186,602. In such use, a composition ofthis invention and at least 3 mole percent of a cognate europiumcompound or the oxide requisite for its formation are finely ground,intimately mixed and heated under the reaction conditions previouslydescribed. For example, 0.75 mole of Gd O .3WO and 0.25 mole ofE11203.3WO3

can be finely ground, mixed and heated at 1000 C. for four hours toyield the solid solution luminophor Such luminescent compositions emitexceptionally bright red light at room temperature and are remarkablyinsensitive to impurities both during preparation and use.

All the compositions of this invention are also luminescent per se, atlow temperatures. The solid solutions of this invention and Eu O .3WOare luminescent at room I temperatures as well.

Luminescent articles and luminescent compositions can be prepared fromthe aforementioned europiumcontaining solid solutions as well asdirectly from the compositions of this invention. The luminescentarticles can comprise at least one of the aforementioned luminophors,optionally in admixture with conventional luminescent materials,intimately associated or in adherent contact with a protective layer ofa material transparent to radiation emitted by the aforementionedluminophors, that is, visible light. The particular structure of theluminescent articles and the manner in which the luminophor is embodiedtherein depends to a great extent upon the purpose for which sucharticles are to be used. The luminophor, for example, can be embedded inthe transparent material, adhered to one or more surfaces thereof,combined with just sufiicient binder to hold the luminophor particlestogether and sandwiched between two layers of transparent material, or acombination of these. More specifically, for example, in luminescentsigns, the luminophor can 'be embedded in a polymeric materialtransparent to incident and emitted radiation and, for example, used assuch or adhered to a signboard or the like. In fluorescent lights, theluminophor is conveniently merely adhered to the inner surface of afluorescent light tube. In cathode ray tubes, the luminophor can beadhered to the inner surface of the glass face plate and, if desired,additional layers, for example, or polymeric material or aluminumtransparent to incident radiation applied thereover.

The shape of the luminescent articles is not critical. They can be flatas in luminescent signs, or curved as in fluorescent lights, or even inthe form of blocks, rods or cubes which can be used, for example, asraised letters on signs. Examples of luminescent articles prepared inaccordance with this invention are fluorescent lights; luminescentsigns, markers and identification devices; luminescent sheets, films,coatings, and other shaped articles.

Examples of materials transparent to radiation emitted by theaforementioned phosphors are organic polymeric materials such ashomopolymers and copolymers of alkyl acrylates and methacrylates such asmethyl methacrylate; polyvinyl acetate; polyethylene; chlorosulfonatedpolyethylene; polypropylene; polystyrene; polyepoxides, polyesters suchas polyethylene terephthalate; polyacrylonitrile; homopolymers andcopolymers of vinyl chloride; polyvinyl alcohol; cellulose derivativessuch as nitrocellulose and ethyl cellulose; inorganic materials such asvarious glasses, including silicate and borate glasses, and transparentcrystalline materials such as lithium fluoride and sodium chloride; aswell as various compatible mixtures thereof.

dried. When the glass plate is placed over a source of 2537 A.ultraviolet light with the coated surface facing the ultraviolet lightsource, the coating emits bright red light. The product described aboveconsists of luminophor embedded in a protective layer of polymethylmethacrylate Luminescent compositions are generally prepared by which istransparent to both the incident ultraviolet light grinding theaforementioned luminescent materials and and the emitted visible redlight and which is in adherent dispersing them, either alone or togetherwith conventional contact with a second protective layer of glass.phosphors, in a solution or dispersion of a binder, for Instead ofcoating the luminophor above onto a glass example, a binder of one ormore of the aforementioned 10 plate, it can be coated onto a signboard,for example, of materials transparent to the emitted radiation. Theresult- Wood or metal or glass in the form of letters, numbers or ingcompositions can be coated onto a surface, for exdesigns. In a likemanner, the coating composition deample, a signboard, and solventevaporated therefrom scribed above can be used to laminate two layers ofglass to yield a luminescent coating. The concentration of in signs,markers or other indicating devices. Similarly, luminophor in suchcompositions can vary widely, for other polymeric materials such asother polyalkyl acrylates example, from as low as 2% to as high as 90%based on or methacrylates, polystyrene or polyvinyl acetate can be thetotal wei ht of the composition, depending upon the substituted for thepolymethyl methacrylate. proposed use of the composition. Particularmethods for Example 18 fabrication of the aforementioned articles andpreparation 1 h d b h d d of the aforementioned compositions aredescribed in more eXamP e 1 Straws 3 met a y g g detail in copendingapplication Ser. No. 186,602 which fluorescent llghts can be.prep.areEH2 3'3Mo 3 i isincorporatgd herein by referenceL pared as previouslydescribed is finely ground and dis- In the following examples, whichillustrate this invenpersed m a mute lacquel} for,example ofmnfccenulose flon, parts and percentages are by Weight unless otherwiseor ethyl cellulose. If desired, in order to obtain a color indicatfidbalance, other luminophors such as manganeseand anti- Examples I 1.016mony-activated calcium halophosphates can also be dispersed therein. Theresulting lacquer is next run through The compositions shown in thefollowing examples are a standard glass fluorescent light tube and thecoating made by the following method, illustrated for Sc O .3WOdeposited on the inside surface thereof is dried. Next,

Sc O (0.3586 part) is intimately mixed with W0 the coated tube is heatedto the temperature, usually (1.6879 parts). About 1% paraffin is addedas a binder somewhat greater than 700 C., at which the cellulose and themixture pressed into pellets. These pellets are la uer i burned off andthe tube somewhat softened, heated in air in a platinum vessel for fourhours at 1000" th th oat d tube i cooled, For a standard 40-watt ri gthe heating the p is burned y- Th light (120 cm. long, 3.8 cm. dia.),about 1 to 4 grams of mixture is converted into the compound Sc O .3WOfor luminophor are deposited as just described, depending which theX-ray diffraction pattern is given in Table I and u o th arti le size ofthe luminophor. The resulting the hysical properties in Table IV. Thecompositions product consists essentially of particles of luminophor 0fthe other examplfis are Similarly P p eXCePt that firmly adhered to theinner surface of a tubular protective [116 1110110 3 wmpounds wereheated at 1490 C layer of glass. The remaining components of thefluoresfour hours and all the M00 compounds were heated at cent light,including the electrodes, terminals, mercury, 900 C. for four hours.etc., are assembled in the conventional manner.

TABLE W Lumi- DGSCGUCG Example Rare Weight Other Weight M.P. Density,Rating 1 N 0. Earth (Parts) Oxide (Parts) Product; C.) g./cc. Color at77 K. Oxide Radiated with 2,537 A.

0.3586 W05 1. can; SC203.3\VO3 4 1.000 W03 0. 5603 3SCZOQLVVO3 5 0.7094W03 1. 2094 EuzOsBWOa 5 0.0957 W03 1. 2335 Gd2033v0x 5 O. 7179 W031.1686 Lu20a 3WO3 5 1.2270 W03 0. 8347 Lazoawoi 4 1. 2033 W03 0. 7990GdQOiWOi 5 0.3193 MOO; 1.0000 $0203.3M0O3 3 0. 3151 M003 1.0000 131103301003 5 0.8395 M003 1.0000 0020 301003 5 0.9210 M003 10000 1112033101003 2 0. 6519 M003 0. 5758 LazO 2MoO 5 8: }wo. 0. 0492(LfiossSmonQzOzBWO; 5 8: Wm 0. 0492 (Lau.00 Y0.01)2Os-3WO3 5 3 338 }W0i0.6 9 t cioiismmiiotswoi 5 i5 {333g 333g }WO3 0.0492 e iiifinyoiinosawoi5 1 Qualitative rating wherein 0 represents no observable luminescence,1 represents feeble luminescence, etc., and 5 represents brightluminescence.

The following examples illustrate preparation of luminescentcompositions and articles fabricated therewith.

Example 17 0.5 part of Eu O .3WO are added to 10 parts of a 20% solutionin methyl ethyl ketone of polymethyl methacrylate and thoroughly blendedto produce a homogeneous slurry. The resulting coating composition ofthis invention is applied to the surface of a glass plate andL112033MOO3 (Gd Sm 203.3W03 and (Gd1 DYX)ZO3.3WO3 Whfil'ein x is fromabout 0.01 to 0.10.

2. A luminescent Sc O .3WO

3. A luminescent 3SCZO3.WO3.

4. A luminescent Eu203.3WO3.

5. A luminescent Gd O .3WO

6. A luminescent L11203-3WO3.

7. A luminescent 8. .A luminescent Gd O .WO

9. A luminescent SC2O3.3MOO3.

composition having composition having composition having compositionhaving composition having composition having composition havingcomposition having 10. A luminescent composition having EU2033MOO3.

11. A luminescent composition having Gd203-3MOO3.

LU2033MOO3.

the

the

the

the

the

the

the

the

the

the

formula formula formula formula formula formula formula formula formulaformula formula 8 13. A luminescent composition having the formulaL212O3.2M0O3- 14. A luminescent (La Sm 2O3.3WO3 0.10.

15. A luminescent 1x yx) 2 3- 3 0.10.

16. A luminescent composition having the formula (Gd Sm O .3WO wherein xis from about 0.01 to 0 10 composition having the formula wherein x isfrom about 0.01 to composition having the formula wherein x is fromabout 0.01 to A luminescent composition having the formula (Gd Dy O .3WOwherein x is from about 0.01 to 0.10.

References Cited Hoffman, Lexikon der Anorganischen Verbindungen, Band2, AlX, No. 56-81, 1914, pages 625 and 747-751.

Kroger, Some Aspects of the Luminescence of Solids, Elsevier Pub. Co.Inc., New York, 1948, pages 109, 110, 286, and 288-298.

Partington, Textbook of Inorganic Chemistry, Sixth.

Edition, Macmillan & Co. Ltd., London, 1950, page 819. Pascal, NouveauTrait de Chimie Minerale, Tome VII, Deuxiame Fascicule, 1959, pages947-953.

Sneed et al., Comprehensive Inorganic Chemistry, D.

' Van Nostrand Co., Inc., New York, 1955, Volume IV,

1. A LUMINESCENT COMPOSITION SELECTED FROM THE GROUP CONSISTING OFSC2O3.3WO3, 3S2O3.WO3, EU2O3.3WO3, GD2O3.3WO3, LU2O3.3WO3, LA2O3.WO3,GD2O3.WO3, SC2O3.3MOO3, EU2O3.3MOO3, GD2O3.3MOO3, LU2O3$3MOO3LA2O3$2MOO3, (LA1-XSMX)2O3$WO3, (LA1-XDYX)2O3$3WO3 (GD1-XSMX)2O3$3WO3AND (GD1-XDYX)2O3$3WO3 WHEREIN X IS FROM ABOUT 0.01 TO 0.10.